The weapon was federal surplus given to the department by the state Office of Emergency Services, L.A. County Sheriff's Department spokesman Steve Whitmore told KPCC. Hundreds of them are given to the department every year, which Whitmore said is particularly helpful during tough budget times.

"This one we believe went missing around the first part of February of this year, and it's obviously an embarrassment, and it obviously just shouldn't happen," Whitmore said.

The OES has suspended the department's ability to receive surplus weapons until it can prove they know where all those weapons are at any given time, Whitmore said.

"Now, how it actually went missing, we don't know yet," Whitmore said. "Where it went missing from, we're not exactly sure. We do have an idea, but we want to continue to dig a little deeper into that."